Core-shell microstructures in 0.68Pb(Fe2/3W1/3)O3-0.32PbTiO3 at the morphotropic phase boundary

The domain structures of ceramics with the morphotropic phase boundary (MPB) composition 0.68PFW-0.32PT were analysed in situ by TEM as a function of temperature from 16 to 300 K. A core-shell structure was detected at room temperature, in which the core of the grains was Ti rich and the shell W rich with respect to the bulk composition. At 16 K, a macrodomain state is observed throughout the volume of the grains, but at >250 K a domain-free shell is formed around a central core that still exhibits strong domain wall strain contrast in two-beam conditions. The presence of the core-shell microstructure and the growth of the core on cooling is correlated with the appearance of (h00)/(00l) peak splitting in XRD traces as temperature decreases and is used to interpret the dielectric data